Photon correlation spectroscopy is being used to study normal hemoglobin (HbA) and sickle cell hemoglobin (HbS) in both the oxy and the unliganded forms. The z-average diffusion coefficients and the polydispersity are determined as functions of the concentration and the temperature. Physiological concentrations can be studied by using a He-Ne laser (633 nm) for the oxy-hemoglobins. For the unliganded forms, longer wavelengths of radiation are required. The diffusion coefficients turn out to be the same for oxy-HbA and oxy-HbS up to concentrations of 36 weight percent. Also, it is found that the diffusion coefficient has a linear dependence on the concentration.